In an essence, League of Legends is a rapidly growing DotA clone that inspires to have it's own unique heroes, mechanics, maps and feel then the normal revamped DotA clones such as Heroes of Newerth and DotA 2. It follows the standard gameplay mechanics that you and 4 other players go against another team of 5 players, all using "champions" that level up throughout each game, gaining ability, item and stat levels. The overall goal is to push the towers of the opposing team and destroy their nexus.

The game is huge. Tournaments, sponsorships, live streams and advertisements are to be found everywhere about this game and that's most likely due to the more casual feel while still catering to the hardcore competitive MOBA players. About 30 million users were counted as registered in April 2012 but it's possible a few hundred thousand are "smurf" accounts or alts.

When you start the game you'll be prompted to enter your experience with past MOBA games, pick your summoner icon and enter your name. Your experience with past MOBA games will help judge what players you're matched up with to begin, your summoner icon can be changed whenever you want and your name can be changed through purchasing Riot Points with real money.

Anyways, you have a level that follows you through your whole account life, being your summoner level, and it will help determine what "runes" you can use, summoner spells, certain features like ranked games and unlocking a point you can assign into a skill tree up until level 30, being the max.

A warning before playing, most people you find in-game will be extremely rude and ignorant so it's suggested you play with friends if possible.

I also suggest that when beginning you try to do some Co-Op Vs AI, allowing you and other players to go against bots, letting you familiarize with the game mechanics.

That's pretty much the gist of the game and I'll help you guys get started by providing some somewhat in-depth roles and what you should be looking to do, along with in-game terms that you'll find when playing.

Tutorial

Terms;

SS/MIA/MISS - Means the enemy has left their lane and/or is not visible. Usually a warning that they are coming to attack another lane.

Gank - An unexpected, coordinated attack from your team/the enemy.

Ward - Pretty much self explanatory. Wards give vision over the map.

CS - Creep score, this means how many minions you have obtained the last hit on.

Feeder/Feeding - Dying a lot of times to the enemy team.

Fed - You have obtained a lot of creep score, gold, or champion kills, putting you at an advantage of power.

Jungler/Jungle - Refers to the Jungle where the neutral minions/buffs spawn
at. Each team has their own jungle and champions can be set up to not lane and level in the jungle. This will be seen a lot later on.

Tank - A champion that can absorb a lot of damage while having some sort of crowd control (cc) to initiate a fight/hold aggro.

Caster/AP-Carry - A champion focused strictly on Ability Power, also known as a "mage" in most other games.

Healer/Support - A champion that will maintain wards and mostly be focused around auras and support items, dedicated to helping the team.

AD Carry/DPS - AD stands for Attack Damage, meaning physical damage.
Champions that do a lot of physical damage will most of the time be
considered an AD "Carry".

Carry - A champion that starts off rather weak but can end up winning the game through farming and killing champions, eventually becoming the strongest in long lasting games. Relates to being "Fed".

Damage Soak - While not usually noted in any match, a damage soak is similar to a tank except for the fact he has no real Crowd Control (cc) and usually ends up mindlessly running around in a fight.

DoT - Damage over Time, found on abilities that have bleeds or anything that does damage over a period of set time.

Top/Middle/Bottom lane - These are lanes that are usually set out before the game starts/at the beginning. Your team will discuss who is going in which lane, usually two top, one middle and two bottom. If your team has a jungler, top will only have one person.

CC - Stands for Crowd Control, counts toward anything that manipulates enemy champions and makes them lose their ability to fight for the duration. They range from Taunts, Stuns, Polymorhs, Knockups and many more.

Zoning - Denying the enemy you're laning against XP/GOLD by pushing them out of range of your minions. This can be done by "harassing".

Harassing - Attacking the enemy laner with abilities/basic attacks in hope to damage and put a hole in their laning phase.

Those are the basic terms you'll find dedicated mostly to MOBA type games. Below, I will dedicate a bit of writing to picking your champion and team composition, along with good and bad lane composition.

You have 5 spots on each team and you have had to think at some point that there is a better combination then just randomly picking. The IDEAL combination is usually seen as this..

AP-Carry Middle Lane

Solo-Top

Jungler

AD Ranged Bottom with a Support/Healer/Tank

While this is ideal, you will not see it a lot in your first few games. Mainly because nobody knows about the correct team composition but also because new players are afraid to try and jungle or find that being a support is boring.

I will describe to you, if you had an ideal team composition, how each lane is roughly played.

For solo top it's difficult. It's basically you against the other top lane, sometimes 1v2 and other times 1v1 with the risk of the enemy jungler ganking you. You must try to stay alive, get a lot of last hits on enemy minions, protect your tower from being pushed, ward your river to make sure you don't get unexpectedly ganked and if possible deny the enemy you're laning against of XP/GOLD by zoning them and/or killing them. This is a more advanced and independent role so I wouldn't suggest taking it if you are new as your team will be counting on you to not lose it. People with the ability to last hit minions well and sustain themselves are usually found here, along with potential carries.

Jungling is also difficult as you must know what you are doing. You rotate through the neutral minions that spawn to level and gain gold while looking for opportunities to help gank lanes in need of help. Jungling can pay off very well if done right as you're potentially getting the same EXP as a solo lane and offering another player on your team to get a solo lane, basically giving you three people that can be a higher level instead of one. Jungling goes very in-depth so I'd look into a guide or write up on one of the links provided at the bottom of this post.

Bottom Lane is divided into two parts; AD Ranged/DPS and Support.
As a support you want to get your laning partner fed by letting them get the last hits on minions and if possible letting them get the last hit on champion kills. It's your job to keep him healed up if possible and/or sustained. It is also your job to provide wards for the entire game around the map, which will be explained in a link provided at the bottom, as well as a few wards early game in the bush by the river of your lane to make sure you don't get ganked.

As the AD Ranged/DPS it is your job to snowball. You must get as much farm from getting last hits as possible as you're the biggest hope in carrying your team. It's fairly simple mechanics, but play it safe and try not to die a lot.

That's mainly the roles, they don't always have to be so static especially in pubs but you'll see it a lot in ranked games.

For a few suggestions, read below.

Starting items - It's best for a new player to start with the recommended items in the shop but I'm letting you know now, starting off with a dorans item isn't the best idea. They don't build into anything else and barely give you any sustain for early laning. For a better start, I suggest getting boots/health potions or something situational to who you think you're going to be laning against. This will save you 350 or so gold into one of your major items.

Get fed; Get cocky - When you get fed you'll feel like you can kill anyone. Let me tell you this now, it's not always true. If you get cocky after being fed you will most likely fall off. Play it cool until you're SURE you can, lets say, solo two people, instead of going in, getting stunned, then dying. Dying WILL put you behind a lot because for that 30 seconds you're doing nothing, essentially being AFK. You lose out on a lot of gold and EXP.

Wards - Wards are Important and ARE needed in any real game. For 75 gold, essentially 3 minion last hits, you get vision over ANY area you place the ward in for 3 minutes. That is a huge advantage.

Be nice to your team - In a game as competitive as this you'll see a lot of hate. Let me tell you this now. You will be mocked and made fun of if you have a semi-competent team and you start blaming everyone else and yelling at them. If you're nice to your team and ask POLITELY to buy a ward, stop dying so much, be more careful, they will definitely respond in a better way. Everyone has bad games.

Amumu is okay, I got to play him either last week or the week before that when he was on the free trial.

You should try out Fiddlesticks, his 2nd spell is called drain and basically can take out 1000+ HP and convert it to yourself, it's great for start game ganks and amazing when you use his ult to teleport to people then use both the spells at the same time.

Ryze is completely overpowered, with the right equips I can one hit combo people at end-game when they have around 3k+ hp.

Look into the melee characters that don't use mana too, they are good.